Si(114)-2×1 표면에서 CaF2의 해리와 선택적 흡착

김희동,Otgonbayar Dugerjav,서재명 한국물리학회 2012 새물리 Vol.62 No.11

Using scanning tunneling microscopy, a CaF_2 molecule on Si(114)-2×1 held at 500 $^\circ$C has been found to dissociate to Ca and F atoms during the initial adsorption stage. The Ca atoms form isolated silicide molecules while the F atoms are desorbed from the surface. For CaF_2coverages up to 0.1 nm in addition to these silicide molecules, a one-dimensional facet composed of CaF(113) and Si(115) planes is formed adjacent to etch pits induced by F atoms. These results imply that F atoms act as an etchant on Si(114) and that CaF is adsorbed selectively on the (113)plane. 가열된 Si(114)-2 ×1 기판 위에 CaF_2를 흡착시킬 경우 초기단계에서는 해리되어 F는 표면에서 탈착하고 Ca 원자만 표면의 Si과반응하여 고립된 실리사이드 분자를 만드는 것을 주사 터널링 현미경을이용하여 초고진공 하에서 관찰하였다. CaF_2의 증착량이 0.1 nm에이르면 이들 Ca 실리사이드 분자 외에도 F에 의하여 에칭이 일어나기판이 파이고 그 주위에 CaF(113) 면과 Si(115) 면으로 이루어진 일차원나노 패싯이 형성된다는 사실을 확인하였다. 결과적으로 Si(114)위에서는 CaF_2 층이나 CaF 층이 직접적으로 형성되지 못하고 (113)면이 형성된 다음에야 CaF 층이 그 위에 성장됨을 본 연구를 통하여규명하였다.

Hot Metal Desulfurization by CaO–SiO₂–CaF₂–Na₂O Slag Saturated with MgO

Cho, Moon Kyung,Cheng, Jin,Park, Joo Hyun,Min, Dong Joon The Iron and Steel Institute of Japan 2010 ISIJ international Vol.50 No.2

<P>The effect of CaF<SUB>2</SUB> and Na<SUB>2</SUB>O on the sulfide capacity of the CaO–SiO<SUB>2</SUB>–CaF<SUB>2</SUB>–MgO<SUB>satd.</SUB>(–Na<SUB>2</SUB>O) slags for hot metal desulfurization was investigated at 1623 and 1723 K by taking the role of MgO as an important refractory component into account. The liquidus line of the MgO-saturated system was similar to the CaO–SiO<SUB>2</SUB>–CaF<SUB>2</SUB> ternary slag system. The silica content for the 2CaO·SiO<SUB>2</SUB>-saturation was slightly decreased with MgO saturation. Although the sulfide capacity at MgO-saturation is lower than that of the CaO<SUB>satd.</SUB>–SiO<SUB>2</SUB>–CaF<SUB>2</SUB> slag system, it is greater than the ternary slag system saturated with 2CaO·SiO<SUB>2</SUB> phase. This suggests that MgO can increase the activity of free O<SUP>2−</SUP> ions under conditions of relatively low CaO activity. Near the composition of 3CaO·SiO<SUB>2</SUB>-saturation, MgO decreased the sulfide capacity of the slag because MgO is less basic than CaO in highly basic compositions. In addition, the addition of 5 mass% Na<SUB>2</SUB>O significantly increases the sulfide capacity of the MgO-saturated slag especially in the composition of low ‘CaO+CaF<SUB>2</SUB>’. This suggests that the input amounts of ‘CaO+CaF<SUB>2</SUB>’ can be reduced from 95 to 75 mass% for maintaining the sulfide capacity of 0.01 at 1623 K, which is important considering the reduction of CaO and CaF<SUB>2</SUB> consumption in hot metal desulfurization process with MgO saturation.</P>

Er3+이 도핑된 유리-세라믹 제조와 1550 nm 여기광에 의한 강한 660 nm 상방전환 형광발생

송수아,유미연,정홍명,김동선,임기수 한국물리학회 2013 새물리 Vol.63 No.6

In this work, we synthesized oxyfluoride glass with a composition of SiO2-Al2O3-CaF2-(CaO) doped with Er3+ ions and prepared glass ceramics containing CaF2 nanocrystals by using proper thermal treatments for infrared-to-visible upconversion emission. Due to the Er ions doped inside the CaF2 nanocrystals, the overall intensity at 660 nm from the glass ceramics was improved by several hundred times compared with that from Er-doped glass under 1550-nm excitation. In addition, the red emission band become narrower and split due to the Er3+ environment. Participation of CaO and Yb3+ ions also contributed to the enhancement of the upconverted emission. Yb3+ ions did not absorb 1550 nm light but interacted with the Er ions. We ascribed the improved emission to several different energy transfer mechanisms to populate the 4F9/2 level of the Er ions. 본 논문에서는 SiO2-Al2O3-CaF2-(CaO) 성분의oxyfluoride 유리에 Er3+ 이온을 도핑하고 적절한 열처리를 이용하여 CaF2 결정이 내부에 형성된 유리-세라믹을 제조하고적외선-가시광선 상방전환 형광 발생을 조사하였다. CaF2 나노결정을 이용함으로써 1550 nm의 적외선 여기광으로 발생하는 Er3+ 이온의4F9/2로부터의 적색형광의 세기가 나노결정이없는 재료에 비해 수백 배 증가한 상방전환을 관측하였고 형광의 띠폭의현저한 감소로 인해 Er3+ 이온이 CaF2 내부에 있음을 확인하였다. 또한 CaO의 존재 유무와 Yb3+이온의 추가 여부에 따른 660 nm 상방전환 형광에 미치는 영향을 검토하였다. Yb3+ 이온은 1550 nm 여기 광을 흡수할 수 없으나Er3+ -Yb3+이온의 상호 에너지전달로 인해 Yb3+이온으로 인한 형광효율이 크게 증가하였고 CaO의참여 역시 형광효율을 크게 향상시켰으며 이러한 결과에 관여한 에너지전달 과정을 분석하였다.

CaF₂ 두께 변화에 따른 ZnS/CaF₂/ZnS/Cu 다층 박막의 광특성

김준식,장건익,Kim, Jun-Sik,Jang, Gun-Eik 한국전기전자재료학회 2009 전기전자재료학회논문지 Vol.22 No.7

Layered ZnS/$CaF_2$/ZnS/Cu film was deposited on glass substrate by using evaporation method. ZnS and $CaF_2$ were chosen as high and low refractive materials. Cu was used as mid-reflective layer. Reflectance with different optical thickness of $CaF_2$ ranging from $0.25{\lambda}\;to\;0.5{\lambda}$ were systematically investigated by using spectrophotometer. In order to expect the experimental results, the simulation program, the Essential Macleod Program(EMP) was adopted and compared with the experimental data. Based on the results taken by spectrophotometer, the ZnS/$CaF_2$/ZnS/Cu multi-layered thin film show the maximum reflectance of 80% at 625nm $(0.25{\lambda}\;in\;CaF_2)$ and 42% at 660nm $(0.5{\lambda}\;in\;CaF_2)$ respectively. As compared with the experimental results and simulation data, it was confirmed the experimental data is well matched with the EMP data.

Effect of CaF₂ and Li₂O Additives on the Viscosity of CaO–SiO₂–Na₂O Slags

Kim, Hyuk,Sohn, Il The Iron and Steel Institute of Japan 2011 ISIJ international Vol.51 No.1

<P>High aluminum containing steels react vigorously with silica-based mold fluxes to form alumina. The change in alumina content increases the viscosity and thus silica-based mold fluxes are compensated with significant amounts of Na<SUB>2</SUB>O, CaF<SUB>2</SUB>, and Li<SUB>2</SUB>O to ensure both lubrication and heat transfer control. Detailed viscosity studies using the rotating spindle method showed that additions of CaF<SUB>2</SUB> up to 8 wt% in the CaO–SiO<SUB>2</SUB>–12wt%Na<SUB>2</SUB>O system at a constant CaO/SiO<SUB>2</SUB> ratio of 0.8 decreases the viscosity by breaking the network structure of molten fluxes, but is negligible above 8 wt%. A similar modification of the network was observed for Li<SUB>2</SUB>O up to 2 wt%. The viscosity data was correlated with the XPS analysis and verified CaF<SUB>2</SUB> and Li<SUB>2</SUB>O as effective in modifying complex silicate structures into simpler silicate structures depending on the availability of complex silicates and thus was limited to below certain concentrations.</P>

Thermodynamics of fluoride-based molten fluxes for extraction of magnesium through the low temperature solid oxide membrane (LT-SOM) process

Lee, Yumin,Yang, Jae Kyo,Park, Joo Hyun Elsevier 2018 CALPHAD, computer coupling of phase diagrams and t Vol.62 No.-

<P><B>Abstract</B></P> <P>The melt quenching experiments and thermodynamic calculations of phase diagrams were carried out to investigate potential additives for the low temperature solid oxide membrane (LT-SOM) magnesium extraction process. The solubility of MgO, which is a major source of magnesium extraction, was also measured in the molten fluoride fluxes. The solubility of MgO in the 46.5MgF<SUB>2</SUB>-46.5CaF<SUB>2</SUB>-7LiF and 45MgF<SUB>2</SUB>-45CaF<SUB>2</SUB>-10NaF (wt%) systems reached 3.4 and 1.9 wt% at 1473 K, respectively, and 1.5 wt% MgO in both fluxes at 1223 K. In addition, the 45MgF<SUB>2</SUB>-55CaF<SUB>2</SUB> binary eutectic flux, which has been widely used in SOM process, could dissolve up to 2.3 wt% MgO at 1473 K. This value is significantly lower than the literature value, <I>i.e.</I> 10 wt% MgO. From the evaluation of the activity coefficient of MgO in the 46.5MgF<SUB>2</SUB>-46.5CaF<SUB>2</SUB>-7LiF and 45MgF<SUB>2</SUB>-45CaF<SUB>2</SUB>-10NaF fluxes under MgO saturation, it was confirmed that the stability of MgO in the 7LiF flux is greater than that in the 10NaF flux. Hence, the driving force of MgO dissolution into the 7LiF flux is higher than that into the 10NaF flux. The newly developed molten flux for magnesium extraction using the LT-SOM process with an operating temperature lower than 1273 K is the 46.5MgF<SUB>2</SUB>-46.5CaF<SUB>2</SUB>-7LiF system.</P>

TiO2가 첨가된 oxy-fluoride 계 유리의 발광특성에 미치는 열처리 효과 연구

우희수,강승구 한국결정성장학회 2020 한국결정성장학회지 Vol.30 No.6

In this study, the optical properties of CaF2-Al2O3-B2O3-TiO2 (CABT) system glass doped with rare earth ion,that is used in various light devices due to its excellent luminous properties, were analyzed as a function of kind of crystal phases formed and size of crystals generated in the glass matrix. TiO2 was added to control nucleation and crystallization,and Eu2O3 was added to enhance the luminescence characteristics. DTA analysis was performed to confirm the heat treatment condition o f crystal generation, and XRD and SEM analysis w ere carried out f or the crystal phase change of nanometer size. As a result of the analysis, the luminous properties of oxy-fluoride-based glass were improved duo to crystallization of nanometer size, but was rather degraded when excessively large crystals were generated. 본 연구에서는 광 발광특성이 우수하여 각종 광장치에 사용되고 있는 CaF2-Al2O3-B2O3-TiO2(CABT) 계 유리의 열처리 조건 및 결정상 생성에 따른 광학적 특성을 연구하였다. CAB 유리의 핵형성 및 결정성장을 제어하기 위해 핵형성제TiO2를 첨가하고, 발광 특성을 향상시키기 위해 희토류 이온 Eu2O3를 첨가하였다. 열처리 조건에 따른 결정 성장 특성을 확인하기 위해 DTA 분석을 수행하였으며, 이에 따른 나노 크기 결정상 변화에 대한 XRD 및 SEM 분석을 수행하였다. 분석 결과 100 nm 크기의 결정생성은 발광강도를 향상시키지만 그 이상의 큰 결정 입자생성은 오히려 발광 특성을 저하시켰다.

광학응용 CaF₂ 단결정성장을 위한 열역학적 공정설계

정성민 ( Seong-min Jeong ),전해진 ( Hae-jin Jeon ),신윤지 ( Yun-ji Shin ),최형석 ( Hyoung-seuk Choi ),배시영 ( Si-young Bae ) 한국전기전자재료학회 2023 전기전자재료학회논문지 Vol.36 No.2

Calcium fluoride (CaF₂) single crystal is applied to numerous industrial applications, especially for optical uses. To have excellent optical transmission properties, however, CaF₂ crystals should be carefully fabricated through liquid-phase crystal growth techniques. In this study, as one of the early stage research activities to grow CaF₂ crystals with a good transmittance at the ultraviolet wavelength range, computational thermodynamic models were provided to deepen the understanding of the crystal growing processes of CaF₂ under various conditions. To remove point defects and oxygen impurities in the grown CaF₂ crystals, the system was thermodynamically evaluated to get optimal process conditions. From the reviews of previous experimental studies, computational thermodynamic approaches were found to be an effective and powerful tool to understand the meaning of the crystal growth processes and to obtain optimal process conditions.

Solubility of TiO2 in NaF‑CaF2‑BaF2 Melts

Jeong‑Hyun Yoo,Sung‑Wook Cho 대한금속·재료학회 2018 METALS AND MATERIALS International Vol.24 No.6

The solubility of TiO2in NaF-CaF2-BaF2 ternary eutectic melts was investigated at the temperature range of 1025–1150 °C. The least-squares equation was obtained from the relationship between the reciprocal temperature and the natural logarithm ofthe titanium concentration in the melts saturated with TiO2. The corresponding partial molar enthalpy of dissolution of TiO2was found to be 188 kJ/mol. The titanium saturation concentration was 3.73 wt% at 1100 °C. From the titanium concentrationchange with the added amount of TiO2at different holding time after a final stirring, it was found that not only completedissolution of TiO2but also enough sedimentation of excessive TiO2should be guaranteed to obtain more reliable solubilitydata. The holding time of 10 h was found to be enough for the excessive TiO2particles to settle down in our experimentalconditions. It is noteworthy that in case of adding TiO2in excess of its solubility, the Ba1.12(Ti8O16) phase was observed atthe lower and bottom of the solidified salt ingots.

PABP Cooperates with the CCR4-NOT Complex to Promote mRNA Deadenylation and Block Precocious Decay

Yi, Hyerim,Park, Joha,Ha, Minju,Lim, Jaechul,Chang, Hyeshik,Kim, V. Narry Elsevier 2018 Molecular cell Vol.70 No.6

<P><B>Summary</B></P> <P>Multiple deadenylases are known in vertebrates, the PAN2-PAN3 (PAN2/3) and CCR4-NOT (CNOT) complexes, and PARN, yet their differential functions remain ambiguous. Moreover, the role of poly(A) binding protein (PABP) is obscure, limiting our understanding of the deadenylation mechanism. Here, we show that CNOT serves as a predominant nonspecific deadenylase for cytoplasmic poly(A)<SUP>+</SUP> RNAs, and PABP promotes deadenylation while preventing premature uridylation and decay. PAN2/3 selectively trims long tails (>∼150 nt) with minimal effect on transcriptome, whereas PARN does not affect mRNA deadenylation. CAF1 and CCR4, catalytic subunits of CNOT, display distinct activities: CAF1 trims naked poly(A) segments and is blocked by PABPC, whereas CCR4 is activated by PABPC to shorten PABPC-protected sequences. Concerted actions of CAF1 and CCR4 delineate the ∼27 nt periodic PABPC footprints along shortening tail. Our study unveils distinct functions of deadenylases and PABPC, re-drawing the view on mRNA deadenylation and regulation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The human CCR4-NOT complex is a predominant nonspecific deadenylase </LI> <LI> PAN2/3 trims excessively long tails with minimal impact on mRNA stability </LI> <LI> CAF1 trims PABPC-free A tails while CCR4 removes PABPC-bound A tails </LI> <LI> PABPC facilitates mRNA deadenylation while preventing precocious uridylation and decay </LI> </UL> </P> <P><B>Graphical Abstract</B></P> <P>[DISPLAY OMISSION]</P>